1. Field of the Invention
The present invention relates to a device and a method for driving an electric actuator such as a motor or a solenoid.
2. Description of the Related Art
In order to make an actuator output a prescribed torque or output power, it is necessary to supply the actuator via a driving circuit with a prescribed amount of current. However, as the output power of the driving circuit is increased, the heat value of the driving circuit increases. Therefore, it is necessary to design a heat radiation structure that corresponds to the output power of the driving circuit.
An actuator and its driving circuit, such as disclosed in JP-A-2001-58578, are separately manufactured. When such an actuator and a driving circuit are picked up from production rots to be combined to put into operation, tuning is necessary so that the actuator can output a prescribed torque because of variations of the actuator in size, resistance, material, etc. In other words, the driving circuit is required to have an excessive amount of output power capacity for the electric actuator to operate as desired.
For example, driving current of a DC motor, as one of the above stated actuator, has a linear relationship with the driving force of the motor, as shown by dotted lines in FIG. 6. When a driving circuit is designed, a minimum amount of the driving current of about 1.7 amperes for a target driving force of about 3 kgf has to be taken into account. In other words, such a driving circuit is designed to provide, as a target driving force, about 5 kgf when driving current of about 2.1 amperes is supplied to the motor. Because it is necessary to have a tolerance in amount of the input current, the maximum amount of the input current may become about 2.5 amperes. In that case, because joule heat generated in the motor increases at a rate of (2.5/1.7)2, it is necessary to make the driving circuit have a large heat sink or a large heat radiation surface.